Coupling agents are commonly used in polymers prepared by anionic polymerization for the formation of a completed polymer. For example, in the formation of polymers, copolymers, and block polymers a first polymer segment or polymerized portion can be prepared, and rather than completing the formation of the polymer via sequential polymerization, a coupling agent can be provided which “couples” the prepared segments together. Multifunctional coupling agents have been used, for example, including silicon halides, polyepoxides, polyisocyanates, polyketones, polyanhydrides, dicarboxylic acid esters. Additionally, divinylbenzene (“DVB”) is a known polyalkenyl coupling agent, and has been used for the preparation of conjugated diene polymers, i.e., styrenic block copolymers as well as polymers of conjugated dienes.
Coupling agents should be sufficiently reactive to couple at least two living polymer arms (same or different) to form a coupled polymer. The coupled polymer can form a linear polymer. Additional arms may also form, e.g., where the coupling agent forms a core onto which a large number of living polymer arms are attached, thus forming a multi-armed polymer. Further, during any such reaction some of the polymer arms may fail to couple, thus causing a portion of the polymer to be coupled and a remaining portion uncoupled.